The wheel bearing apparatus is used to rotationally bear a wheel of a vehicle and roughly classified to a driving wheel use and a driven wheel use. In general, due to structural reasons of the wheel bearing apparatus, the inner ring rotation type is adopted for the driving wheel bearing apparatus and both the inner ring rotation type and the outer ring rotation type are adopted for the driven wheel bearing apparatus. In general, the double row angular contact ball bearings with low rotational torque features are used for many uses. Some of the reasons are that they have a desirable bearing rigidity, exhibit excellent durability against misalignment from the point of view of fuel consumption. In the double row angular contact ball bearing, a plurality of balls is interposed between a stator ring and a rotational ring. The balls contact the rings while the rings apply a predetermined contact angle onto the balls.
In the wheel bearing apparatus with the double row rolling bearing, it has become desirable in recent years to improve fuel consumption for resource savings or antipollution. Especially, it is important to reduce the weight of the wheel bearing apparatus while keeping both its strength and rigidity. To solve such a problem, an outer member (stator ring) of the wheel bearing apparatus shown in FIG. 11 has been proposed.
In this wheel bearing apparatus, strength and rigidity are improved by modifying the configurations or dimensions of only a weakest part of an outer member 51. The weakest part is determined by previously obtaining stresses generated in parts of a body mounting flange 52 by an FEM analysis when a moment load is applied to the outer member 51. That is, four bolt insertion holes 53, 54 are formed on the body mounting flange 52. The thickness of peripheral portions A, B of an upper side, a side opposite to a road surface, and the thickness of peripheral portions C, D of a lower side, road surface sides, is differentiated. More particularly, a thickness A1 of the peripheral portions A, B of the upper side, where a load is applied so as to separate the peripheral portions A, B from a knuckle 55 (shown by a two-dot chain line), is larger than the thickness B1 of the peripheral portions C, D of the lower side, where a load is applied so as to push the peripheral portions C, D toward the knuckle 55 as shown in FIG. 11(b).
This makes it possible to provide a wheel bearing apparatus with a long service-life that satisfies the contradictory problems. It balances them at high level since the body mounting flange 52 is formed so that only the part required for the strength and rigidity is thickened and the other part is thinned. See, JP2009-292370 A.
In such a wheel bearing apparatus, the roundness of outer raceway surfaces 51a, 51a of the outer member 51, after mounting of the wheel bearing apparatus, is largely influenced by the thickness of the knuckle 55. That is, the outer raceway surface 51a, especially one near the knuckle is largely influenced by the knuckle55when the thickness of the knuckle55is larger than the thickness A1 of the outer member body mounting flange 52. Accordingly, if the contact state of abutment surfaces, such as a configuration or contact area of the abutment surfaces, is not good, deterioration of the roundness of the outer raceway surfaces may not be prevented by taking measures only on the bearing portion.
Corresponding to the circumstances, a wheel bearing apparatus is known that prevents the outer raceway surface of the outer member from being influenced by strain, tensile stress, caused by uneven contact between the stator flange of the outer member and the knuckle. As shown in FIG. 12, the wheel bearing apparatus has a body mounting flange 68 of a noncircular configuration. Larger diameter portions 71 and smaller diameter portions 72 are alternately arranged along a circumference of an outer member 70.Mounting holes 73 are formed in the larger diameter portions 71. As shown in FIG. 13, circularly continued recessed grooves 74 are formed on base-end side portions, radially inner-side portions, of an inner-side surface 69, surface to be faced to a knuckle 75, of the larger and smaller diameter portions 71, 72. A radially outer-side edge of the recessed groove 74, formed on the larger diameter portions 71, is positioned at the same or a radially outer position of the radially outer-side edge of the recessed groove 74 formed on the smaller diameter portion 72.
As shown in FIGS. 13(a) and 13(b), each of the recessed grooves 74is formed to have a configuration recessed toward a direction apart from an outer-side surface 75a of the knuckle 75, the left in FIG. 13. The deepest portions 76 of the recessed grooves 74 exist in both the larger and smaller diameter portions 71, 72.
Under the circumstances, the inner-side surface 69 of the body mounting flange 68 and the outer-side surface 75a of the knuckle 75 contact each other at portions other than the recessed grooves 74. That is, since the recessed groove 74 is also formed on the inner-side surface of the smaller diameter portion 72, the smaller diameter portion 72 does not contact the outer-side surface 75a of the knuckle 75. Only portions around the mounting holes 73 of the larger diameter portions 71 contact the outer-side surface 75a of the knuckle 75. Accordingly, it is possible to reduce the contact area between the body mounting flange 68 and the knuckle 75. Thus, it is possible to reduce the degree of influence on the accuracy of the outer member 70 even if the finishing accuracy of the outer-side surface 75a of the knuckle 75 is not good.
In addition, the recessed groove 74 formed on the base of the body mounting flange 68 is more easily elastically deformable than other portions of the body mounting flange 68. Thus, it is possible to absorb the strain of the body mounting flange 68 even when strain is caused by uneven contact condition between the inner-side surface 69of the body mounting flange 68 and the outer-side surface 75a of the knuckle 75.Thus, it is possible to prevent the outer member outer raceway surfaces, not shown, configuration accuracy, including roundness, from being adversely affected. See, JP2012-228909 A.
However, in the prior art wheel bearing apparatus, the recessed grooves 74 are insufficient to prevent the roundness of the outer member outer raceway surfaces from being adversely affected. This is due to the flatness of turning machined abutment surface of the knuckle 75a being inferior, and that the strength and durability of the body mounting flange 68, itself, would be degraded by the recessed grooves 74 formed on the inner-side surface 69 of the body mounting flange 68.